Steps to reproduce
1. Create a new project, and remove everything from the scene (or alternatively, download the attached project).
2. Disable both realtime and baked GI options in the Lighting window.
3. Make sure that the Profiler window is open.
4. Press Play in the editor.
5. Notice the CPU utilization in the Global Illumination section in Profiler.

Expected behavior
With all the lightmapper options disabled, CPU should not be utilized by GI related tasks.

Actual behavior
CPU utilization by GI-related tasks sometimes reaches 1ms.

Notes
• Tested in Unity 2017.3.0p3, 5.6.5.p1, 2017.2.0f3, 2018.1.0b9.
• Clearing baked data, GI cache (both within Unity and manually), and removing the lightmap folder does not fix the issue.
• Restarting the editor does not help.
• The issue affects both Scene and Game modes.
• The issue is not present in standalone builds.